The goal of this project is to determine the crystal structure of the enzyme uroporphyrinogen decarboxylase (Uro-D). Uro-D function in the heme biosynthetic pathway, catalyzing four successive decarboxylation reactions at different sites of the substrate. Using a rotating anode source, we have collected data from crystals of native and selenomethionylated protein. Multiwavelength data collection at SSRL is expected to allow elucidation of this important structure. This result will advance understanding of the apparently novel mechanism of this critical enzyme.